Catalysis of addition reactions



' material.

Patented Mar. 13, 1951 Chemical Elaborations, Inc a. corporation ofDelaware r OFFICE Pa., assignor to Philadelphia, Pa.,

N Dati g. Application October 8, 1947, v Serial No. 778,721

. 1 This invention ielatesitd addition reactionsfof organic" compounds,and; more" particularly, I to qend h' 'a o r t o s b dje s f i, lt sknln' h,a a t i rod cts a b ehtained'; for example, by condensa tion' ofone' alde hyde melecule on. another, when thematerial is treated with'an'alkalifcatalyst. Dilute caustic or alkali acetates are themostirequently used J, ,.,n:;l .I'I ,i 7 However, the yields obtained withthese catalysts havenot been satisfactory, and it has been fiw telf hfibsre$ y e, reaction- Eor'exampla the icla'ssic alfmethod" of producing anethil fii t ylfa i.2 mr ente =r isto heat .propionaldehyde"in admixture'withfa concentrated (47%) aqueous solution of sodium acetate.Propionaldel'iyde is slightly, solub n such asolution, and as aresultfthe' ad'- r'hii'itur'e consists substantially of an emulsion. Duetothe poor ,contactfbetween the aldehyde and the catalyst, the" reactionis very slow. The yield ofdimer is unsatisfactory. i

In addition, the sodium acetate reaction" is hazardous, since theemulsion has'a tendency to break downyreleasing propionaldehyjde, whichfloats on top of, the acetate solution. When this condition exists, theactate solution may be raised to a temperature considerably above theboiling point-of the propionaldehyde, which, as a consequence, maylbeabruptly vaporized;with resulting damage to the apparatus and loss of Ageneral object of the present invention is to attain smooth control ofaddition reactions and particularly of aldol condensations. a

A more specific object of the invention is to produce high yields ofa-methyl-p-ethyl acrolein from propionaldehyde conveniently and withaccurate control of the reaction productsf attain these objects byemploying as a catajfor the'aldol condensation an aqueous solution. ofan alkali metal's oap-of a higher fatty acid; j

7 According tothe invention, the soap is used in aqueous solution whoseconcentration may vary according to 1 the -starting--materials= and alsoaccordingitothe end "product: desired. For example, when formingthe-unsaturated dimer of propionaldehyde, I prefer to use aconcentration ofbetween .10 and 30% soap. The starting materialisdissolved in about an equal volume of the soap solution, and refluxeduntil th'e additi'on reaction has gonefto-completion as indicated by theleveling 01fof the boilingpoint of the mate- 9 Claims. (Cl. 260 601)rial. Depending upon the innermtakerifor treatment, this may requirefrom i to-15 hours.

As is known, the saturated dimer of propional dehyde I(Z-methyl-3-hydroxy-valeric-aldehyde) is dehydrated concurrently withits formation to th -fit ac e n-"y V, r The new aldehyde isonly'slightly soluble-in the soap solution, and will'be observed "tocollect above the soap. The major portionof the reacted material maytherefore-be physically separated from the soap solution, and thebalance steam distilled therefrom. Alternatively the reacted material,still in; th'e'soapsolution,fmay be transferred to a stainless steelstill-kettlewhich is'heated with steam until all of the volatilematerials are distilled over. Thedistillate is then driedandfractionated. The scan solution remaining after the distillation may berecharged with solid soap and employed in the next run.

I have found that the sodium soaps are most satisfactory forthepropionaldehyde condensation, and that, of these, sodium stearate(pH9.45) is the most generally available and gives excellent results. Asa matter of fact I have found that the universally available hard whitesoap of commerce affords a cheap and convenient source of this material.

Whatever the source, the soap employed must be of reasonable purity,and, specifically, must contain no freealkali, since the high pH of freealkali apparently catalyzes the reaction of trimers and higher polymers,and, in fact, introduces many of the diiiiculties inherent in the priorart processes. I

The concentration of soap in the soap solution depends to considerableextent upon the material being treated and'the end product desired. Theminimum concentration is ordinarily limited by the solubility of thestarting material, that is, the soap solution must be strong enough tocompletely dissolve the starting materials. On the other hand, I havefound that with very concentrated soap solutions the reaction'may be toovigorous, or that the addition reaction will be extended toproduceflargermolecules than desired. Between these two extremes, which,of course, vary with difierent materials, there is'an optimumconcentration which aflords excellent control of the progress of thereaction. Itshould perhaps'be pointed out that within this rangeeconomic considerations may locate tration somewhat away from the pointof optimum conversion. For example, when it is desiredto take advantageof thefact that the soap is not affected by the reaction and may be usedthe concern then placed in a stainless steel was observed to rise over aperiod over again, it is preferable to operate at a rela-- tively lowconcentration to avoid the formation of high molecular weight compounds,since the unreacted material may be recycled and ultimately converted tothe desired end product.

The yields obtained depend upon the concentration of the, soap solution,the ratio of soap solution to raw material, the particular soap 'used asa catalyst, and the temperature of the then allowing the solution tocool.

5210 grams of propionaldehyde (approximately 90 moles) was mixed with anequal volume of the soap solution and agitated until a clear mixture wasobtained. It should be emphasized at this point that it is highlyimportant that the propionaldehyde-soap mixture be present in the formof a single clear phase. The solution was still-kettle fitted with anefficient reflux condenser. The temperature was gradually raised to theneighborhood of 60 C. at which temperature the mixture of soap andpropionaldehyde started to boil.

As the reaction progressed, the boiling point of about 8 hours, finallyleveling offat about 90 C., at which time the heating was terminated.The material was transferred to a separatory funnel and the floatinglayer of reacted material removed. The balance of the soap solution wastransferred to a distillation kettle of stainless steel and steamdistilled to recover the dissolved material. The total product, afterhaving been dried with anhydrous sodium sulfate, was distilled directlyfrom a Claissen flask.

The distillate was divided into three fractions and a residue, whichwere then refractionated in accordance with orthodox technique torecover 3528 grams of material exhibiting a constant boiling point ofl3'7.3 C. The theoretical conversion, calculated upon the basis of 5210grams (the weight of the original material) less 810 grams (the weightof 45 moles of water lost in the dehydration of the saturated dimer),equals 4400 grams. The conversion actually realized, namely, 3628 grams,therefore, represented 82.4% of the theoretical conversion.

It should be pointed out that the low boiling fractions obtained duringthe distillation are recycled in the practice of the invention, andthat, accordingly, the overall yield of a continuous process will behigher than the conver sion effected in a single reaction. It shouldalso be mentioned that the apparatus used has a pronounced effect uponyield; for example, when employing glass apparatus with conventionalsealed joints, the loss of material due to the volatility ofpropionaldehyde reduced the conversion per cycle to figures in theneighborhood of 50% of the theoretical conversion.

The remaining soap solution was preserved, and upon being reinforcedwith solid soap to restore the concentration to 20%, was available foruse with a new charge of propionaldehyde.

I have observed that when the concentration of soap is increased beyond30%, the conditions were found to favor the formation of trimers. On theother hand, when the concentration of soap is reduced below 10%, thepropionaldehyde does not completely dissolve.

It should be pointed out that the raw material taken for treatment, forinstance, the propionaldehyde described in the example reported above,should be of reasonable purity and should be acid free to avoidreleasing the fatty acid from the soap.

Among the advantages of the invention may be mentioned the following:

The alkali metal and the fatty acid comprisingthe soap may be selectedto give the precise pI-Imost suitable for the production of a particularcondensation product. For example, when a higher pH is desired,potassium soaps may be employed, or weaker acids, such as myristic acid,may be used in forming the soap. On the other hand, when a lower pH isdesirable, the sodium soaps of stronger acids, such as oleic acid, maybe used. Thus, according to the invention, a

large part of the reacting material may be obtained in the form of acompound of a given molecular weight.

The soap employed as a catalyst in the present invention is an excellentsolvent for the raw materials, with the result that the reaction time isdrastically reduced.

The excellent solvent characteristics of the soap solution alsoeliminate the hazard of superheating of the liquid reactants duringrefluxing. The solvent action of the soap is. selective to the extentthat the condensation product is readily separable from the soapsolution.

According to the invention, therefore, it is possible to effect thereaction smoothly and to convert a substantial portion of the rawmaterial to the desired end product.

It should be stated in conclusion that the high degree of controlinherent in the invention is especially adapted to the formation ofdimolecular aldehydes.

I claim:

1. The method of preparing a-methyl-fi-ethyl acrolein which comprisesdissolving propionaldehyde in about an equal volume of a 10 to 30%aqueous solution of sodium stearate, refluxing until the, boiling pointof the mixture reaches C1., and fractionally distilling the mixture toobtain a product having a constant boiling point at l3'7.3 C.

2. The process of preparing a-methyl-B-ethyl acrolein which comprisesheating propionaldehyde in admixture with an equal volume of an aqueoussolution comprising 10 to 30% sodium stearate by weight.

3. The method of producing a-methyl-p-ethyl acrolein frompropionaldehyde which comprises refluxing a mixture of propionaldehydeand an aqueous solution of sodium stearate for a length of timesuflicient to raise the vapor temperature to about 90 C.

4. The process which comprises dissolving propionaldehyde in a 20%aqueous solution of sodium stearate, refluxing until the boiling pointof the solution reaches about 90 C. and isolating a-methyl-c-ethylacrolein.

5. The method of producing a-methyl-fi-ethyl acrolein which comprisesrefluxing a mixture of propionaldehyde and an aqueous solutioncomprising from 10 to 30% of a commercial hard white soap for a lengthof time sufficient to raise the. vapor temperature to about 90 C.

6. The method of producing a-HlthYl-B-GthYl acrolein frompropionaldehyde which comprises heating a mixture of propionaldehyde andan aqueous solution of sodium stearate of from to 30% concentration byweight at a temperature in excess of 60 C. for from 1 to 10 hours.

7. The method of producing dimeric aldehydes which comprises'refiuxingavolume, of a monomeric aldehyde dissolved in about an equal volume ofan aqueous solution of an alkali metal soap of a higher fatty acid,terminating the reaction after a portion of the monomer is condensed tothe dimer, isolating said dimer from the mixture of monomer and soap,reenforcing said mixture with additional monomer and soap, and repeatingthe operation.

8. The method which comprises refluxing a mixture of propionaldehyde andabout an equal volume of a 10 to 20% aqueous solution of sodium stearateat a temperature between 60 'C'. and 90 C. until a portion of thepropionaldehyde is condensed to methyl ethyl acrolein, isolating saidmethyl ethyl acrolein, charging the remainder of said mixture with freshpropionaldehyde and sodium stearate, and recycling said mixture.

6 9. The method of producing a-methyl-p-ethyl acrolein which comprisesthe steps of refluxing a volume of propionaldehyde dissolved in about anequal volume of an aqueous solution of an.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Fischer etal Feb. 4, 1941 OTHERREFERENCES Lieben et al., Monatschefte f. Chemie, vol. 4, pages 16 to 21(1883).

Number

2. THE PROCESS OF PREPARING A-METHYL-B-ETHYL ACROLEIN WHICH COMPRISESHEATING PROPIONALDEHYDE IN ADMIXTURE WITH AN EQUAL VOLUME OF AN AQUEOUSSOLUTION COMPRISING 10 TO 30% SODIUM STEARATE BY WEIGHT.